Optical dry-films and methods of forming optical devices with dry films

ABSTRACT

Provided is a dry-film suitable for use in forming an optical component. The dry-film includes a carrier substrate having a front surface and a back surface. A negative-working photoimageable polymeric layer is disposed over the front surface of the carrier substrate, and includes a photoactive component and units of the formula (RSiO 1.5 ), wherein R is a substituted or unsubstituted organic group. In each of the units, R is free of hydroxy groups. The units include units of the formula (R 1 SiO 1.5 ) and (R 2 SiO 1.5 ), wherein R 1  is a substituted or unsubstituted aliphatic group and R 2  is a substituted or unsubstituted aromatic group. A protective cover layer is disposed over the front surface or back surface of the carrier substrate. Also provided are methods of forming optical devices with dry-films. The invention finds particular applicability in the optoelectronics industry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Application Nos. 60/638,458, filed Dec. 22, 2004,and 60/659,353, filed Mar. 7, 2005, the entire contents of whichapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of optoelectronics.In particular, the present invention relates to dry-films which aresuitable for use in forming optical components such as waveguides. Aswell, the invention relates to methods of forming optical componentswith a dry-film. The invention additionally relates to methods offorming electronic devices such as printed wiring boards having opticalfunctionality.

Signal transmission using pulse sequences of light is becomingincreasingly important in high-speed communications and data transfer.For example, optical integrated circuits are gaining importance for highbandwidth optical interconnects. As a result, the integration of opticalcomponents such as waveguides, filters, optical interconnects, lenses,diffraction gratings, and the like, is becoming increasingly important.

The incorporation of optical layers in the form of embedded opticalwaveguides into printed wiring boards is known. For example, U.S. Pat.Nos. 6,731,857 and 6,842,577 to Shelnut et al, disclose embedded opticalwaveguides formed using silsesquioxane chemistry on a printed wiringboard substrate. The optical waveguides include a core and a cladsurrounding the core, with optical radiation propagating in the core dueto its higher index of refraction as compared to the clad.

Embedded optical waveguides are typically formed by coating a bottomclad layer over a substrate, coating a core layer over the bottom cladlayer, patterning the core layer to form a core structure, and forming atop clad layer over the bottom clad layer and core structure. The bottomclad, core and top clad layers may be formed from compositions in liquidform which include solvent and polymer components. Where the waveguidesare to be formed as part of a printed wiring board, use by the boardmanufacturer of a specialized coating tool such as a roller coater,curtain coater, slot coater or spin-coater is typically required. Oncethe liquid composition is coated, the solvent is removed from thecoating by a drying process. The solvents used in the liquidcompositions may be flammable and/or explosive in nature, and mayadditionally be deemed environmental pollutants. As a result, boardmanufacturers must take measures to contain or treat the solvent andmaintain its vapor concentration at safe levels. Such measures include,for example, solvent collection, incineration with or without catalyticconverters and use of explosion-proof equipment. The costs associatedwith these activities can be significant. It would thus be desired forcomponent manufacturers to have at their disposal an optical materialwhich is in an easily-applicable form and is solvent-free or extremelylow in solvent-content.

Formation of optical waveguides on a printed wiring board using a seriesof pre-cast, or dry-film, layers has been proposed. For example,International Publication No. WO 03/005616 discloses methods of formingmulti-level printed wiring boards that integrate optical datacommunications with other boards without electrical connections. Opticalwaveguides are formed on the printed wiring board by laminating theentire top surface of the printed wiring board with a first polymericoptical conductive layer, a second, higher refractive index polymericlayer, and a third layer of the first layer polymer material. Asunderstood, the disclosed polymeric material is acrylate-based. Thereare, however, various drawbacks associated with the use of acrylates informing optical components. For example, acrylates are generally notsuitable for use in high temperature applications, for example, inchip-to-chip applications. At temperatures approaching 200° C., mostacrylate materials begin to decompose and depolymerize. Moreover,acrylates are structurally and optically dissimilar to glass, which isthe current material of choice for optical fibers and pigtailstructures.

The aforementioned U.S. Pat. No. 6,731,857 discloses silicon-basedphotoimageable waveguide compositions which can be coated as a dry-film.The disclosed compositions include silsesquioxane units of the formula(RSiO_(1.5)), wherein R is a side chain group selected fromhydroxyphenyl and hydroxybenzyl. It is believed that suchhydroxy-containing side chain groups contribute to optical loss due tolight absorption, for example, at 1550 nm which is a commonly usedwavelength in the optoelectronics industry.

There is thus a need in the art for optical dry-films and for methods offorming optical components which overcome or conspicuously ameliorateone or more of the foregoing problems associated with the state of theart.

SUMMARY OF THE INVENTION

A first aspect of the invention provides dry-films suitable for use informing optical components. The dry-films include a carrier substratehaving a front surface and a back surface. A negative-workingphotoimageable polymeric layer is disposed over the front surface of thecarrier substrate, and includes a photoactive component and units of theformula (RSiO_(1.5)), wherein R is a substituted or unsubstitutedorganic group. In each of the units, R is free of hydroxy groups. Theunits include units of the formula (R¹SiO_(1.5)) and (R²SiO_(1.5)),wherein R¹ is a substituted or unsubstituted aliphatic group and R² is asubstituted or unsubstituted aromatic group. A protective cover layer isdisposed over the front surface or the back surface of the carriersubstrate.

In a second aspect of the invention, methods of forming an opticaldevice are provided. The methods involve applying over a first substratea dry-film that includes a carrier substrate and a negative-workingphotoimageable polymeric layer. The photoimageable polymeric layerincludes a photoactive component and units of the formula (RSiO_(1.5)),wherein R is a substituted or unsubstituted organic group. In each ofthe units, R is free of hydroxy groups. The units include units of theformula (R¹SiO_(1.5)) and (R²SiO_(1.5)), wherein R¹ is a substituted orunsubstituted aliphatic group and R² is a substituted or unsubstitutedaromatic group. At least a portion of the photoimageable polymeric layeris then exposed to actinic radiation.

In a third aspect of the invention, optical components such as opticalwaveguides may be formed using the described dry-films and methods. Thedry-films may be used in forming a waveguide core and/or clad.

In a fourth aspect of the invention, the dry-films and methods of theinvention may be used to form an electronic component such as a printedwiring board that includes optical functionality, for example, in theform of embedded optical waveguides.

As used herein, the terms “polymer” includes oligomers, dimers, trimers,tetramers and the like, and encompasses homopolymers and higher orderpolymers, i.e., polymers formed from two or more different monomer unitsand heteropolymers. The terms “a” and “an” are inclusive of “one ormore”. The term “on” and “over” are used interchangeably in definingspatial relationships, and encompass the presence or absence ofintervening layers or structures. Unless otherwise specified, amountsfor components of the compositions are given in weight % based on thecomposition absent any solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed with reference to the followingdrawings, in which like reference numerals denote like features, and inwhich:

FIGS. 1A-C illustrate exemplary optical dry-films in accordance with theinvention; and

FIGS. 2A-F illustrate an exemplary printed wiring board having opticalfunctionality at various stages of formation thereof in accordance withthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to FIG. 1,which illustrates in cross-section an exemplary dry-film 1 in accordancewith the present invention. The inventive dry-films are suitable for usein forming optical components, such as optical waveguides, filters,optical interconnects, lenses, diffraction gratings, and the like. Theillustrated dry-film 1 includes a carrier substrate 2, anegative-working photoimageable polymeric layer 4 over the front surfaceof the carrier substrate, and a protective cover layer 6. The protectivecover layer 6 may, for example, be disposed on the front surface of thedry-film over the polymeric layer 6 as shown in FIG. 1A or on the backsurface of the dry-film as illustrated in FIG. 1B. Use of a back surfaceprotective cover layer may be desired, for example, where multipledry-film sheets are arranged in a stacked arrangement or if the dry-filmis stored in roll-form 8 such as shown in FIG. 1C.

The carrier substrate 2 typically functions as a mechanical support forthe polymeric layer 4 and any other layers of the dry-film duringmanufacture, storage and subsequent processing. The carrier substrate 2may be removed from the remainder of the dry-film in subsequent use, ormay form part of the final structure of the device fabricated. Where thecarrier substrate is eventually removed from the dry-film such as bypeeling, adhesion between the carrier substrate and the remainder of thedry-film is typically low to moderate to allow for ease in separation.In cases in which the carrier substrate is to form part of the finaldevice, adhesion is typically high to prevent peeling of the carriersubstrate. The particular material used for the carrier substrate mayvary widely. The material may be natural or synthetic and may be capableof existing in a flexible or rigid film/sheet form. Suitable carriersubstrate materials include, for example: polyethylene terephthalate(PET), typically an optically pure PET, which may be treated in variousways, for example, resin-coated, flame or electrostaticdischarge-treated, or slip-treated; a paper such as polyvinylalcohol-coated paper, crosslinked polyester-coated paper,polyethylene-coated paper, cellulose paper, or a heavy paper such aslithographic paper; nylon; glass; cellulose acetate; a synthetic organicresin; a polyolefin such as polypropylene; a polyimide; a polyurethane;a polyacrylate such as polymethylmethacrylate (PMMA); fiberboard; ametal such as copper, aluminum, tin, magnesium, zinc, nickel, or analloy thereof; and a multilayered structure of two or more of these orother materials, for example, a copper-coated fiberboard or epoxylaminate. The carrier substrate typically has a thickness, for example,of from about 25 to 250 μm.

The photoimageable polymeric layer 4 is of a material making it suitablefor use in forming an optical component. For example, in the case of anoptical waveguide, the polymeric layer has particular applicability informing the waveguide core and/or clad. The polymeric layer is formedfrom a composition that includes silsesquioxane units of the formula(RSiO_(1.5)), wherein R is a substituted or unsubstituted organic group.In each of the silsesquioxane units, R is free of hydroxy groups. It isbelieved that as a result of the hydroxy-free side chain groups, opticalloss characteristics can be improved over materials usinghydroxy-containing side chain groups. The silsesquioxane units includeunits of the formula (R¹SiO_(1.5)) and (R²SiO_(1.5)), wherein R¹ is asubstituted or unsubstituted aliphatic group and R² is a substituted orunsubstituted aromatic group. The presence of both aliphatic andaromatic silsesquioxane units in the composition is believed to resultin a polymer having properties which are more desirable than thoseresulting from aliphatic-only or aromatic-only silsesquioxane units. Forexample, the presence of aliphatic groups is believed to provide forgreater cross-linking density and/or enhanced dissolution in a developersolution, while aromatic groups are believed to result in a more tough,crack-resistant polymer. The composition further includes a photoactivecomponent and other optional components. Further details of compositionsuseful in forming the polymeric layer 4 are provided below. Thethickness of the polymeric layer 4 is typically from about 5 to 150 μm.

The protective cover layer 6 provides protection to the polymeric layer4, and is typically in the form of a removable film or sheet that may bepeeled from the remainder of the dry-film. In the exemplified dry-filmof FIG. 1A, adhesion of the protective cover layer 6 to the polymericlayer 4 is less than that of the carrier substrate 2 to the polymericlayer. This allows for separation of the protective cover layer from thepolymeric layer without also separating the polymeric layer from thecarrier substrate. Suitable materials for the protective cover layerinclude, for example, polyolefins such as polyethylene andpolypropylene, polyvinyl alcohol, and PET. The protective cover layer 6typically has a thickness of from about 10 to 100 μm. Optionally, theprotective cover layer may include a first layer coated with a releaselayer which contacts the polymeric layer. Suitable release layermaterials include, for example, thermally or photochemically curedsilicones, polyvinyl stearate, polyvinyl carbamates, polyN-ethyl-perfluoroactyl sulfanamidoethyl methacrylate, poly(tetrafluorothylene), polypropylene, polymethyl methacrylate,polysiloxanes, polyamides, and other release materials such as thosedescribed in Satas, Handbook of Pressure Sensitive Adhesive Technology,2^(nd) ed., Van Nostrand/Reinhold (1989). As described above, theprotective cover layer 6 may be formed on the back surface of thecarrier substrate 2 as shown in the exemplary dry-film of FIG. 1B. Thesame materials described above with respect to the protective coverlayer and release layer may be used for this purpose. The protectivecover layer may itself be in the form of a release layer such asdescribed above, formed on the back surface of the carrier substrate.U.S. Pat. No. 6,057,079 to Shelnut, the contents of which areincorporated herein by reference, describes suitable back surfacerelease coatings which may be used in the optical dry-films of thepresent invention. The protective cover layer may further be formed bysurface treating the back surface of the carrier substrate to producerelease characteristics with respect to the polymeric layer, forexample, by altering the surface states of the carrier substrate backsurface.

The dry-films in accordance with the invention may be prepared, forexample, by coating the composition for the polymeric layer onto acarrier substrate, for example, by meniscus coating, spray coating,roller coating, wire roll coating, doctor blade coating, curtain coatingand the like, typically to a dry thickness of from 5 to 150 microns. Thecoated carrier substrate may be dried, for example, by convectiondrying, infrared drying, air drying and the like, typically to a solventcontent of from 0 to 10 wt %, typically less than 5 wt % or from 2 to 5wt %, based on the polymeric layer.

The carrier substrate may be in the form of discrete sheets, typicallyfrom 2 to 150 cm in width and from 2 to 150 cm in length, which may becoated and dried as sheets and stacked. The carrier sheet may further bein the form of a roll, typically from 2 to 150 cm in width and from 0.5to 1000 meters in length, which may be coated and dried in areel-to-reel format, commonly known as a web coating process. Theprotective cover layer may be applied, for example, by lamination withor without heat and/or pressure. The sheets may be stacked or the webrolled with a front surface or back surface protective cover layer toseparate the sheets or wraps.

The invention further provides methods of forming an optical deviceusing a dry-film as described above. Briefly stated, the methods involveapplying over a first substrate a dry-film that includes a polymericlayer on a carrier substrate such as described above, and exposing atleast a portion of the polymeric layer to actinic radiation.

FIGS. 2A-F illustrates an optical waveguide structure on a printedwiring board at various stages of formation thereof. While the inventionis described with reference to this exemplary embodiment, it should beclear that optical components other than waveguides may be formed, suchas filters, optical interconnects, lenses, and diffraction gratings.Similarly, electronic substrates other than printed wiring boardsubstrates, such as semiconductor wafers, and non-electronic substratesmay be employed.

As shown in FIG. 2A, a printed wiring board substrate 10 is provided.The printed wiring board substrate may be, for example, a laminatedsheet that includes a series of epoxy resin and copper layers on whichetched electronic circuits, conductive traces and electronic componentsare formed or will be formed on one or both sides. Depending on theboard's design, the optical waveguide structure may be incorporated intothe board at an earlier or later stage in the board fabrication process.

The dry-film 1 described above is affixed to the printed wiring boardsubstrate 10 to form an optical waveguide bottom clad layer. Suitabletechniques for affixing the dry-film to the substrate 10 include, forexample, lamination techniques such as hot roll lamination. In theexemplified method, the dry-film 1 is placed into a hot roll laminator,the protective cover layer 6 is peeled away from the polymeric layer 4,and the polymeric layer 4 is brought into contact with and laminated tothe printed wiring board substrate 10 using rollers 11 with heat andpressure. The lamination temperature is typically from about 21 to 150°C., for example, from about 25 to 110° C. The pressure is typically fromabout 0.1 to 5 kg/cm² (1.4 to 71 psi), for example, from about 0.3 to 2kg/cm² (4.3 to 28.5 psi). The speed of the rollers 11 is typically fromabout 1.5 to 600 cm/min, for example, from about 30 to 150 cm/min. Thepolymeric layer 4 is next treated by exposure to actinic radiationfollowed by a thermal cure. The exposure may be a blanket exposure or,alternatively, exposure using a photomask followed by development wherethe bottom clad is to be patterned. Typical curing temperatures are fromabout 120 to 200° C., for example, from about 145 to 180° C., and curingtime is typically from about 0.5 to 5 hours, for example, from about 1to 3 hours. The carrier substrate 2 is typically removed from thepolymeric layer 4 and printed wiring board substrate 10, such as bypeeling, before or after exposure.

With reference to FIG. 2B, a waveguide core dry-film 1′ is next affixedto the bottom clad layer 4 in the manner described above with referenceto the bottom clad dry-film 1. The core dry-film 1′ may have the same orsimilar construction as the bottom clad dry-film 1, except thephotoimageable polymeric layer 12 in the core dry-film should provide arefractive index in the final waveguide structure that is greater thanthat of the cladding.

The second polymeric layer 12 is next patterned as illustrated in FIGS.2C and D. As illustrated, the photoimageable core layer 12 may be imagedby exposure to actinic radiation 14 through a photomask 16, asillustrated in FIG. 2C. Polymerization in the exposed regions of thecore layer 12 decreases the solubility thereof in a developer solution.As shown in FIG. 2D, the unexposed portions of core layer 12 are removedby the developer solution, leaving one or more core structures 12′.

Following formation of core structures 12′, a top clad layer 18 isformed over the bottom clad layer 4 and core structures 12′ byapplication of another dry-film 1″, as shown in FIG. 2E. The samematerials and procedures employed in processing the bottom cladpolymeric layer 4 may be used for the top clad polymeric layer 18. Therefractive index of the top clad polymeric layer 18 in the finalwaveguide structure is less than that of the core structures 12′ and istypically the same as the bottom clad layer 4. A waveguide structure 20including bottom clad layer 4, core structure 12′ and top clad layer 18is thereby formed, as shown in FIG. 2F.

Following formation of the optical waveguide structure on the printedwiring board substrate 10, the printed wiring board may be furtherprocessed. For example, one or more dielectric and/or metal layers maybe formed over the waveguide structure, to form a metallizationstructure for signal routing. Similarly, one or more additional opticallayers may be provided, for example, to form additional opticalwaveguide structures, optical vias or other optical components.Electrically connecting an optoelectronic device such as a photodetectoror a laser emitting device, for example, a VCSEL chip, may also beperformed at this stage. The printed wiring board is processed tocompletion using known techniques such as those described in Coombs,Printed Circuit Handbook, 5^(th) ed., McGraw-Hill (2001).

The dry-film polymeric layer is formed from a composition that includesa polymer component which includes polymerized silsesquioxane units ofthe formula (RSiO_(1.5)), wherein R is a substituted or unsubstitutedorganic group. In each silsesquioxane unit, R is free of hydroxy groups.The silsesquioxane units include one or more units of the formula(R¹SiO_(1.5)) and (R²SiO_(1.5)), wherein R¹ is a substituted orunsubstituted aliphatic group, and R² is a substituted or unsubstitutedaromatic group. The polymer component is typically present in thecomposition in an amount of from 1 to 99.5 wt %, for example from 60 to98.5 wt %.

The aliphatic group may be a straight-chain, branched-chain or cyclicgroup, saturated or unsaturated. Suitable aliphatic groups include, forexample, those having from 1 to 20 carbon atoms, such as methyl, ethyl,propyl, isopropyl, t-butyl, t-amyl, octyl, decyl, dodecyl, cetyl,stearyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, (C₂-C₆)alkenyl, norbonyland adamantyl. The aliphatic group may be substituted, for example,wherein one or more hydrogen atom on the side chain group replaced by aheteroatom or other group, for example, deuterium, halogen such asfluorine, bromine, or chlorine, (C₁-C₆)alkyl, (C₁-C₆)haloalkyl,(C₁-C₁₀)alkoxy, (C₁-C₁₀)alkylcarbonyl, (C₁-C₁₀)alkoxycarbonyl,(C₁-C₁₀)alkylcarbonyloxy, alkylamine, alkylsulfur-containing materials,and the like. Additionally or alternatively, one or more carbon atom inthe alkyl chain may be substituted with a heteroatom such as nitrogen,oxygen, sulfur, phosphorus, and arsenic. Such heteroatom-substitutedaliphatic groups include, for example, piperidinyl andtetrahydrofuranyl.

Aromatic groups which may be used include, for example, those havingfrom 6 to 20 carbon atoms such as phenyl, biphenyl, tolyl, 1-naphthyl,2-naphthyl and 2-phenanthryl. For purposes herein, a side-chain groupthat includes an aromatic constituent is considered an aromatic group.Thus, groups containing both aryl and alkyl components such as benzyl,methylbenzyl and ethylbenzyl are aromatic groups. The aromatic group maybe substituted, for example, wherein one or more hydrogen atom on theside chain group is replaced by a heteroatom or other group, forexample, deuterium, halogen such as fluorine, bromine, or chlorine,(C₁-C₆)alkyl, (C₁-C₆)haloalkyl, (C₁-C₁₀)alkoxy, (C₁-C₁₀)alkylcarbonyl,(C₁-C₁₀)alkoxycarbonyl, (C₁-C₁₀)alkylcarbonyloxy, alkylamine,alkylsulfur-containing materials, and the like. Additionally oralternatively, one or more carbon atom in the aryl group may besubstituted with a heteroatom such as nitrogen, oxygen, sulfur,phosphorus, and arsenic. Such heteroatom-substituted aliphatic groupsinclude, for example, thiophene, pyridine, pyrimidine, pyrrole,phosphole, arsole and furane.

The polymer may take the form of a copolymer or higher order polymer,either random- or block-type. For example, the polymer may include oneor more additional silicon-containing unit such as one or moreadditional unit chosen from silsesquioxanes, cage siloxanes, siloxanesand combinations thereof. For example, the polymer may include one ormore additional unit of the formula (R³SiO_(1.5)), wherein R³ is asubstituted or unsubstituted organic group and is free of hydroxygroups. The polymer may contain, for example, methyl, butyl and phenylsilsesquioxane units; ethyl, phenyl and trifluoromethylphenylsilsesquioxane units or methyl, benzyl and phenyl silsesquioxane units.Suitable siloxanes include, for example, units of the formula((R⁴)₂SiO), wherein R⁴ is a substituted or unsubstituted organic group,such as an alkyl group, for example, methyl, ethyl, propyl, and thelike, or an aryl group, for example, phenyl, tolyl, and the like.

The polymers may contain a wide range of repeating units. Thus, thepolymer may vary widely in molecular weight. Typically, the polymershave a weight average molecular weight (M_(w)) of from about 500 to15,000, more typically from about 1000 to 10,000.

The polymers may include two or more functional end groups that allow asolubility change in the composition after photoactivation. Such endgroups may be, for example, hydroxy; alkoxy such as ethoxy, propoxy,isopropoxy; carboxyester, amino, amido, epoxy, imino, carboxyacid,anhydride, olefinic, acrylic, acetal, orthoester, vinyl ether, andcombinations thereof. The functional end content may be, for example,from about 0.5 to 35 wt % based on the polymer.

The photoimageable polymeric layers formed from the compositions includea component for altering the solubility of the layers uponphotoactivation. The photoactive component alters the solubility of thelayers in a dried state in a developer. The photoactive componenttypically generates an acid or base upon activation. A wide variety ofphotoactive components may be used in the present invention, including,but not limited to, photoacid generators and photobase generators.

The photoacid generators useful in the present invention may be anycompound or compounds which generate acid upon exposure to light.Suitable photoacid generators are known and include, but are not limitedto, halogenated triazines, onium salts, sulfonated esters, substitutedhydroxyimides, substituted hydroxylimines, azides, naphthoquinones suchas diazonaphthoquinones, diazo compounds, and combinations thereof.

Useful halogenated triazines include, for example, halogenated alkyltriazines such as the trihalomethyl-s-triazines. The s-triazinecompounds are condensation reaction products of certainmethyl-trihalomethyl-s-triazines and certain aldehydes or aldehydederivatives. Such s-triazine compounds may be prepared according to theprocedures disclosed in U.S. Pat. No. 3,954,475 and Wakabayashi et al.,Bulletin of the Chemical Society of Japan, 42, 2924-30 (1969). Othertriazine type photoacid generators useful in the present invention aredisclosed, for example, in U.S. Pat. No. 5,366,846.

Onium salts with weakly nucleophilic anions are particularly suitablefor use as photoacid generators in the present invention. Examples ofsuch anions are the halogen complex anions of divalent to heptavalentmetals or non-metals, for example, antimony, tin, iron, bismuth,aluminum, gallium, indium, titanium, zirconium, scandium, chromium,hafnium, copper, boron, phosphorus and arsenic. Examples of suitableonium salts include, but are not limited to, diazonium salts such asdiaryl-diazonium salts and onium salts of group VA and B, IIA and B andI of the Periodic Table, for example, halonium salts such as iodoniumsalts, quaternary ammonium, phosphonium and arsonium salts, sulfoniumsalts such as aromatic sulfonium salts, sulfoxonium salts or seleniumsalts. Examples of suitable onium salts are disclosed, for example, inU.S. Pat. Nos. 4,442,197; 4,603,101; and 4,624,912. Sulfonium salts suchas triphenylsulfonium hexafluorophosphate and mixtures thereof aretypical.

The sulfonated esters useful as photoacid generators in the presentinvention include, for example, sulfonyloxy ketones. Suitable sulfonatedesters include, but are not limited to, benzoin tosylate, t-butylphenylalpha-(p-toluenesulfonyloxy)-acetate, 2,6-dinitrobenzyl tosylate, andt-butyl alpha-(p-toluenesulfonyloxy)-acetate. Such sulfonated esters aredisclosed, for example, in the Journal of Photopolymer Science andTechnology, vol. 4, No. 3,337-340 (1991).

Substituted hydroxyimides which may be used include, for example,n-trifluoromethylsulfonyloxy-2,3-diphenylmaleimide and2-trifluoromethylbenzenesulfonyloxy-2,3-diphenylmaleimide. Suitablesubstituted hydroxylimines include, for example,2-(-nitrilo-2-methylbenzylidene)-(5-hydroxyiminobutylsulfonyl)-thiophene.Azides useful in the present invention include, for example,2,6-(4-azidobenzylidene)cyclohexanone. Naphthoquinones may include, forexample, 2,1-diazonaphthoquinone-4-sulfonate ester of2,3,4-trihydroxybenzophenone. Among the diazo compounds,1,7-bis(4-chlorosulonyl phenyl)-4-diazo-3,5-heptanedione may be used.

Photobase generators useful in the present invention may be any compoundor compounds which liberate base upon exposure to light. Suitablephotobase generators include, but are not limited to, benzyl carbamates,benzoin carbamates, O-carbamoylhydroxyamines, O-carbamoyloximes,aromatic sulfonamides, alpha-lactams, N-(2-allylethenyl)amides,arylazide compounds, N-arylformamides,4-(orthonitrophenyl)dihydropyridines, and combinations thereof.

The amount of photoactive component is any amount sufficient to alterthe solubility of the polymeric layer upon exposure to actinic radiationand render the exposed portion insoluble in a developer. The photoactivecomponent is typically present in the composition in an amount of from0.1 to 25 wt %, for example from 0.1 to 12 wt %.

The developer for the photoimageable polymeric layer may be an aqueousor non-aqueous developer solution, or a combination thereof, and mayoptionally include one or more additives, for example, antifoamingagents, surfactants and the like. Typical aqueous developers include,for example, alkali metal hydroxides such as sodium hydroxide andpotassium hydroxide in water, as well as tetraalkylammonium hydroxidesuch as tetramethylammonium hydroxide, in water. Such developers aretypically used in concentrations from 0.1 to 2N, for example, 0.15 to1N, or 0.26 to 0.7N.

Typical non-aqueous developers include, for example, ketones such asacetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone,2-octanone, 2-heptanone and methyl isoamyl ketone; alcohols such asethanol, isopropanol, n-propanol, n-butanol, isobutanol and benzylalcohol; esters such as ethyl acetate, ethyl propionate and ethyllactate; glycol ethers such as ethylene glycol methyl ether, propyleneglycol ethyl ether, propylene glycol methyl ether; glycol ether esterssuch as ethylene glycol monomethyl ether acetate and propylene glycolmono methyl ether acetate; aromatics such as toluene, xylene,chlorobenzene, dichlorobenzene and the like, and combinations thereof.

Development is typically conducted at a temperature of from 20 to 85°C., for example from 21 to 49° C. Development time with aggressiveagitation may be within ten minutes, for example, within five minutes,within two minutes, within one minute, or within 30 seconds. Developmentmay take place, for example, in a static development chamber or in aspray chamber. Typical spray pressures range from 5 to 40 psi (0.35 to2.8 kg/cm²), for example, from 10 to 25 psi (0.7 to 1.8 kg/cm²).

One or more components for improving the flexibility of the structuresformed from the composition may be present in the composition. Theseflexibility-improving materials typically contain a plurality offunctional groups chosen from hydroxy, amino, thiol, sulphonate ester,carboxylate ester, silyl ester, anhydride, aziridine, methylolmethyl,silyl ether, epoxides, oxetanes, vinyl ethers, silanols and combinationsthereof. In the flexibility-improving materials, the functional groupsare typically attached to backbone materials. Exemplary backbonematerials include substituted and unsubstituted alkyl and arylhydrocarbons, ethers, acrylates, novolacs, polyimides, polyurethanes,polyesters, polysulfones, polyketones, fullerenes, POSS silicons,nanoparticles, and combinations thereof. The functional groups may bepresent as end groups on the backbone and/or at one or more locationsalong the backbone.

Examples of flexibilizing components are polyols of formula R⁵(OH)_(x)wherein R⁵ is an organic group chosen from substituted or unsubstituted(C₂-C₂₅) alkyl, (C₇-C₂₅) aryl, (C₈-C₂₅) aralkyl, (C₆-C₂₅) cycloalkyl,and combinations thereof, wherein x is 2 or more and does not exceed thenumber of carbon atoms. When x is 2, examples of the flexibilizingcomponent include glycols, which are 1,2 diols, such asHOCH₂—CHOH—(CH₂)_(y)—CH₃ wherein y may be, for example, from 0 to 22,such as propylene glycol and butylene glycol. Other examples includeα,ω-diols such as HO—(CH₂)_(z)—OH wherein z is, for example, from 2 to25 such as ethylene glycol, 1,3-propanediol and 1,4-butanediol. When xis 3 examples include glycerin and trimethylolpropane.

R⁵ may also be a polyether of formula —O—(CR⁶ ₂)_(w)— wherein w is, forexample, from 1 to 13 and R⁶ is the same or different and may be, forexample, H, or a substituted or unsubstituted organic group of formulaC₁-C₁₂ alkyl, aryl, aralkyl or cycloalkyl. Examples of flexibilizingcomponents include polyether diols of polyethylene oxide, polypropyleneoxide, polybutylene oxide, and polytetrahydrofurane.

The flexibility-improving component may have a weight average molecularweight, for example, of from 62 to 5000, for example from 62 to 2000.This component may be present in an effective amount to improve theflexibility of the composition in a dried state before and afteractivation. The specific amount will depend, for example on the backboneand type of and number of functional groups of the flexibility-improvingcomponent. This component may, for example, be present in thecomposition in an amount of from 0.5 to 35 wt %, for example from 2 to20 wt %.

In addition to the foregoing flexibilizers, the use of siloxanes such asthose described above with reference to the polymer having units of theformula ((R⁴)₂SiO) may be used.

Other additives may optionally be present in the compositions including,but are not limited to, surface leveling agents, wetting agents,antifoam agents, adhesion promoters, thixotropic agents, fillers,viscosity modifiers, and the like. Such additives are well known in theart of coating compositions. The use of surface leveling agents, forexample silicone-base oils such as SILWET L-7604 silicone-base oilavailable from Dow Chemical Company, in the compositions may be used. Itwill be appreciated that more than one additive may be combined in thecompositions of the present invention. For example, a wetting agent maybe combined with a thixotropic agent. The amounts of such optionaladditives to be used in the present compositions will depend on theparticular additive and desired effect, and are within the ability ofthose skilled in the art. Such other additives are typically present inthe composition in an amount of less than 5 wt %, for example less than2.5 wt %.

The compositions useful in the invention may optionally contain one ormore organic cross-linking agents. Cross-linking agents include, forexample, materials which link up components of the composition in athree-dimensional manner. Aromatic or aliphatic cross-linking agentsthat react with the silicon-containing polymer are suitable for use inthe present invention. Such organic cross-linking agents will cure toform a polymerized network with the silicon-containing polymer, andreduce solubility in a developer solution. Such organic cross-linkingagents may be monomers or polymers. It will be appreciated by thoseskilled in the art that combinations of cross-linking agents may be usedsuccessfully in the present invention.

Suitable organic cross-linking agents useful in the present inventioninclude, but are not limited to, amine containing compounds, epoxycontaining materials, compounds containing at least two vinyl ethergroups, allyl substituted aromatic compounds, and combinations thereof.Typical cross-linking agents include amine containing compounds andepoxy containing materials.

The amine containing compounds useful as cross-linking agents in thepresent invention include, but are not limited to, melamine monomers,melamine polymers, alkylolmethyl melamines, benzoguanamine resins,benzoguanamine-formaldehyde resins, urea-formaldehyde resins,glycoluril-formaldehyde resins, and combinations thereof.

It will be appreciated by those skilled in the art that suitable organiccross-linker concentrations will vary with factors such as cross-linkerreactivity and specific application of the composition. When used, thecross-linking agent(s) is typically present in the composition in anamount of from 0.1 to 50 wt %, for example, from 0.5 to 25 wt % or from1 to 20 wt %.

One or more of the additives may serve to adjust refractive indices ofthe polymeric layers, for example, in the case of an optical waveguide,the core and/or clad layers.

The composition typically further includes a solvent. A wide variety ofsolvents may be used, for example: glycol ethers, such as ethyleneglycol monomethyl ether, propylene glycol monomethyl ether, anddipropylene glycol monomethyl ether; esters such as methyl cellosolveacetate, ethyl cellosolve acetate, propylene glycol monomethyl etheracetate, dipropylene glycol monomethyl ether acetate; dibasic esters;carbonates such as propylene carbonate; γ-butyrolactone; esters such asethyl lactate, n-amyl acetate and n-butyl acetate; alcohols such asn-propanol, iso-propanol; ketones such as cyclohexanone, methyl isobutylketone, diisobutyl ketone and 2-heptanone; lactones such asγ-butyrolactone and γ-caprolactone; ethers such as diphenyl ether andanisole; hydrocarbons such as mesitylene, toluene and xylene; andheterocyclic compounds such as N-methyl-2-pyrrolidone,N,N′-dimethylpropyleneurea; and mixtures thereof.

The following examples are intended to illustrate further variousaspects of the present invention, but are not intended to limit thescope of the invention in any aspect. For purposes of the examples,amounts for the various components are given in weight % based on theentire composition including solvent.

1. Preparation of Optical Dry-Films

EXAMPLES 1-14

The following procedure for forming optical dry-films is employed foreach of Examples 1-14. The components set forth below are combined inadmixture to form a composition. The composition is roller coated onto a50 μm thick polyethylene terephthalate (PET) carrier substrate film to awet thickness of 100 μm and is dried in a convection oven for 30 minutesat 90° C. to a thickness of 50 μm. A 25 μm thick polyethylene (PE)protective cover layer is applied to the surface of the coated layerwith a roller to create a dry-film. The dry-film is wound into a rollconfiguration such as shown in FIG. 1C.

wt % Example 1 (Examples 15, 29) propylene glycol monomethyl etheracetate 45 phenyl-methyl-trifluoromethylsilsesquioxane (47.5:47.5:5.0)54.84 triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604 silicone-baseoil 0.01 Example 2 (Examples 16, 30) propylene glycol monomethyl etheracetate 45 phenyl-methyl-dimethylsilsesquioxane (55.5:39.5:5.0) 54.84triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604 silicone-base oil0.01 Example 3 (Examples 17, 31) propylene glycol monomethyl etheracetate 45 phenyl-methyl-dimethylsilsesquioxane (48:48:2) 54.84triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604 silicone-base oil0.01 Example 4 (Examples 18, 32) propylene glycol monomethyl etheracetate 45 phenyl-methyl-dimethylsilsesquioxane (60:30:10) 54.84triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604 silicone-base oil0.01 Example 5 (Examples 19, 33) propylene glycol monomethyl etheracetate 45 phenyl-methyl-benzylsilsesquioxane (48:48:2) 44.84polytetrahydrofurane 10 triphenylsulfonium tosylate 0.15 Dow SIL WETL-7604 silicone-base oil 0.01 Example 6 (Examples 20, 34) propyleneglycol monomethyl ether acetate 45 phenyl-methyl-dimethylsilsesquioxane(42.5:42.5:15) 54.84 triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604silicone-base oil 0.01 Example 7 (Examples 21, 35) propylene glycolmonomethyl ether acetate 45 phenyl-methyl-dimethylsilsesquioxane(48:48:2) 44.84 polytetrahydrofurane 10 triphenylsulfonium tosylate 0.15Dow SIL WET L-7604 silicone-base oil 0.01 Example 8 (Examples 22, 36)propylene glycol monomethyl ether acetate 45phenyl-methyl-dimethylsilsesquioxane (42.5:42.5:15) 44.84polydiphenylsiloxane 10 triphenylsulfonium tosylate 0.15 Dow SIL WETL-7604 silicone-base oil 0.01 Example 9 (Examples 23, 37) propyleneglycol monomethyl ether acetate 45 phenyl-methyl-dimethylsilsesquioxane(48:48:2) 44.84 polydisiloxane 10 triphenylsulfonium tosylate 0.15 DowSIL WET L-7604 silicone-base oil 0.01 Example 10 (Examples 24, 38)propylene glycol monomethyl ether acetate 45phenyl-methyl-dimethylsilsesquioxane (42.5:42.5:15) 49.84hexamethylolmelamine 5 triphenylsulfonium tosylate 0.15 Dow SIL WETL-7604 silicone-base oil 0.01 Example 11 (Examples 25, 39) propyleneglycol monomethyl ether acetate 50 phenyl-methyl-silsesquioxane (67:33)45.3 Polytetrahydrofurane 4.56 naphthyldiphenylsulfoniumperfluorobutanesulfonate 0.1 Dow SIL WET L-7604 silicone-base oil 0.04Example 12 (Examples 26, 40) propylene glycol monomethyl ether acetate50 phenyl-methyl-dimethylsilsesquioxane (48:48:2) 45.3 polycaprolactone4.56 triphenylsulfonium tosylate 0.1 Dow SIL WET L-7604 silicone-baseoil 0.04 Example 13 (Examples 27, 41) propylene glycol monomethyl etheracetate 45 phenyl-methyl-dimethylsilsesquioxane (48:48:2) 44.84polycaprolactone 10 triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604silicone-base oil 0.01 Example 14 (28, 42) propylene glycol monomethylether acetate 45 phenyl-methyl-dimethylsilsesquioxane (42.5:42.5:15)49.84 glycerine 5 triphenylsulfonium tosylate 0.15 Dow SIL WET L-7604silicone-base oil 0.01

EXAMPLES 15-28

The procedures and materials of Examples 1-14 are repeated, except priorto roller coating, the back surface of the PET substrate is coated witha 5 μm silicone release layer in place of the front surface PEprotective cover layer.

EXAMPLES 29-42

The procedures and materials of Examples 1-14 are repeated, except thesubstrate is 125 μm thick Kraft paper impregnated with polyethylene onits back surface, in place of the front surface PE protective coverlayer.

2. Preparation of Printed Wiring Boards

EXAMPLES 43-61

With reference to Table 1, the following procedures for forming opticalwaveguides on a printed wiring board are employed.

a. Bottom Clad Formation

A 30 mg/cm² copper foil clad printed wiring board containing circuitrythereon is placed in a hot roll laminator. The front surface PEprotective cover layer (if present) is removed from the remainder of thebottom clad (“clad 1”) dry-film set forth in Table 2. The polymericlayer of the dry-film is placed against the copper surface on theprinted wiring board, and the dry-film is laminated to the printedwiring board in the hot-roll laminator at 30 cm/min, 20 psi (1.4kg/cm²), and 100° C. The polymeric layer is blanket exposed to 500mJ/cm² of actinic radiation from a mercury halide lamp. The PET film isremoved from the structure, and the printed wiring board is placed in aconvection oven at 180° C. for 60 minutes to cure the layer, thusforming a bottom clad layer on the printed wiring board.

b. Core Structure Formation

The printed wiring board laminated with the bottom clad layer is placedin a hot roll laminator. The front surface PE protective cover layer (ifpresent) is removed from the remainder of the core dry-film set forth inTable 2. The polymeric layer of the core dry-film is placed against thewaveguide bottom clad layer on the printed wiring board, and thedry-film is laminated in the hot-roll laminator at 30 cm/min, 20 psi(138 kPa), and 100° C. The polymeric core layer is exposed to 500 mJ/cm²of actinic radiation from a mercury halide lamp through a maskcontaining core patterns including openings of from 2 to 30 cm withwidths of from 25 to 250 μm. The printed wiring board is placed in aconvection oven for 20 minutes at 90° C. The PET is removed and theprinted wiring board is placed in a 0.7 N NaOH developer solution for2.5 minutes at room temperature with mild agitation. The printed wiringboard is rinsed in DI water and dried with an air knife. It is thencured in a convection oven at 180° C. for 60 minutes, resulting in aplurality of waveguide cores on the waveguide bottom clad layer.

c. Top Clad Formation

The same procedures described above for the bottom clad layer are usedto form a top clad (“Clad 2”) layer over the bottom clad layer and corestructures, thereby forming a waveguide structure on the printed wiringboard substrate.

TABLE 1 Ex. Dry-Film Ex. Layer 43 1 Clad 1 2 Core 1 Clad 2 44 3 Clad 1 4Core 3 Clad 2 45 5 Clad 1 6 Core 5 Clad 2 46 7 Clad 1 8 Core 7 Clad 2 479 Clad 1 10 Core 9 Clad 2 48 11 Clad 1 12 Core 11 Clad 2 49 13 Clad 1 14Core 13 Clad 2 50 15 Clad 1 16 Core 15 Clad 2 51 17 Clad 1 18 Core 17Clad 2 52 19 Clad 1 20 Core 19 Clad 2 53 21 Clad 1 22 Core 21 Clad 2 5423 Clad 1 24 Core 23 Clad 2 55 25 Clad 1 26 Core 25 Clad 2 56 27 Clad 128 Core 27 Clad 2 57 29 Clad 1 30 Core 29 Clad 2 58 31 Clad 1 32 Core 31Clad 2 59 33 Clad 1 34 Core 33 Clad 2 60 35 Clad 1 36 Core 35 Clad 2 6137 Clad 1 38 Core 37 Clad 2

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made, and equivalentsemployed, without departing from the scope of the claims.

1. A dry-film suitable for use in forming an optical component,comprising: a carrier substrate having a front surface and a backsurface; a negative-working photoimageable polymeric layer over thefront surface of the carrier substrate, comprising a photoactivecomponent and units of the formula (RSiO_(1.5)), wherein R is asubstituted or unsubstituted organic group, and wherein in each of saidunits, R is free of hydroxy groups, and wherein said units compriseunits of the formula (R¹SiO_(1.5)) and (R²SiO_(1.5)), wherein R¹ is asubstituted or unsubstituted aliphatic group and R² is a substituted orunsubstituted aromatic group; and a protective cover layer over thefront or back surface of the carrier substrate.
 2. The dry-film of claim1, wherein the carrier substrate is a polymeric film.
 3. The dry-film ofclaim 1, wherein the dry-film is in a rolled configuration.
 4. Thedry-film of claim 3, wherein the protective cover layer is disposed overthe back surface of the carrier substrate.
 5. A method of forming anoptical device, comprising: (a) applying over a first substrate adry-film comprising a carrier substrate and a negative-workingphotoimageable polymeric layer, the photoimageable polymeric layercomprising a photoactive component and units of the formula(RSiO_(1.5)), wherein R is a substituted or unsubstituted organic group,and wherein in each of said units, R is free of hydroxy groups, andwherein said units comprise units of the formula (R¹SiO_(1.5)) and(R²SiO_(1.5)), wherein R¹ is a substituted or unsubstituted aliphaticgroup and R² is a substituted or unsubstituted aromatic group; and (b)after (a), exposing at least a portion of the photoimageable polymericlayer to actinic radiation.
 6. The method of claim 5, wherein theoptical device is an optical waveguide, the method further comprisingdeveloping the exposed photoimageable polymeric layer, to form anoptical waveguide core structure.
 7. The method of claim 6, furthercomprising providing a bottom clad layer over the first substrate before(a), and providing an upper clad layer over the bottom clad layer andthe core structure.
 8. The method of claim 7, wherein the bottom cladlayer and/or the upper clad layer are formed by applying over the firstsubstrate a respective bottom or upper clad dry-film, comprising acarrier substrate and a negative-working photoimageable polymeric layercomprising units of the formula (R³SiO_(1.5)), wherein R³ is asubstituted or unsubstituted organic group.
 9. The method of claim 8,further comprising exposing the bottom and/or upper clad dry-film toactinic radiation.
 10. The method of claim 5, wherein the firstsubstrate is a printed wiring board substrate.